September 2009Fidelity Potential IndexiPod, MP3, CD, LP, SACD
What Sounds Better and Why.
Article By John Meyer Of Newform Research

The evolution of
high fidelity has followed a generally upward trend with the occasional sidestep
into poorly thought out or poorly supported formats. As the means of reproducing
music has burgeoned, so too has the variety of formats with the consequences of
confusing media incompatibilities and redundant software. Amid this blizzard of
formats, delivery systems and exploding playback options, the holy grail of the
past 80 years of audio enthusiasts of ever higher fidelity has been largely
sidelined in the scramble for market dominance and "accessibility".

But no matter what the format or the listening
environment, sound quality will ultimately have a huge impact on the enjoyment
the listener will get from the music. So to put the evolution of music into
perspective and evaluate the stages, it is important to compare the fidelity
potential of the various formats whether iPod, mp3, SACD or DVD-Audio.
Comparison between analog and digital is difficult. However, it is possible to
establish ranges of equivalence for comparisons among the formats. Below we list
different formats and quantify their potential to deliver sound accurately and
fully to the listener.

Expressing digital in terms of mathematical
quantity is simple but not so for analog whose limits are possible to ballpark
but not to pinpoint. Also, the different formats have different weaknesses
making exact comparison even less precise. However, in broad strokes, comparison
is possible and long overdue. The ongoing debate over the past 25 years as to
which format - analog or digital - "vinyl or CD" -- sounds better has
been conducted in the fog of ignorance and marketing hype. The first digital
format, the CD, was billed as "Perfect Sound Forever" -- fidelity so
high no one human could perceive anything better.

Many people knew at its introduction this was
marketing hyperbole and now everyone knows it. Despite the many hoary flaws in
analog playback that the public found extremely frustrating, the new CD system
clearly had limitations of its own and they weren't all due to poor
implementation.

But the move to digital represented a complete
direction shift for playback systems and perhaps we should not have expected the
new system to be superior in every respect to the old. All things being equal,
the more information a format can transmit, the better the sound will be. So
here are the formats broken down into their bare bit potential some with high
and low ranges. There are a huge number of caveats and remarks about the
formats' various weaknesses but the Fidelity Potential Index gives a reasonable
approximation of the fidelity a particular format is capable of delivering.

Fidelity Potential Index (FPI)
Table

The
Formats

Analog
or Digital

Dynamic
Range

Frequency
Response

Equivalent
Sampling Rate (Hz)

Equivalent
Bits

Bits
per Second

Fidelity
Potential Index

Wax Cylinders

analog

20dB
30dB

160 - 3kHz
160 - 3kHz

6,000
6,000

3.3
5

20,000
30,000

0.2
0.3

AM Radio

analog

48dB

50 - 6kHz

12,000

8

96,000

1

Shellac 78

analog

30dB
40dB

60 - 7kHz
60 - 7kHz

14,000
14,000

5
6.7

70,000
93,800

0.7
0.9

78 rpm Record

analog

40dB

40 - 11kHz

22,000

6.7

147,400

1.5

FM Radio

analog

70dB

40 - 15kHz

30,000

11.7

351,000

3.5

45 rpm Record

analog

45dB

40 - 11kHz

22,000

7.5

165,000

1.7

The Vinyl LP
33rpm

analog

50dB
65dB
75dB

30 - 25kHz
30 - 25kHz
30 - 25kHz

50,000
50,000
50,000

8.3
10.8
12.5

415,000
540,000
625,000

4.2
5.4
6.3

Reel to Reel Tape
Recorder

analog

60dB
70dB

20 - 18kHz
20 - 50kHz

36,000
100,000

10
11.7

360,000
1,170,000

3.6
11.7

Cassette Tape
Recorder

analog

45dB
70dB

40 - 15kHz
40 - 15kHz

30,000
30,000

7.5
11.7

225,000
351,000

2.3
3.5

8 Track Tape

analog

45dB

40 - 8kHz

16,000

7.5

120,000

1.2

The CD Compact
Disc

digital

44,100

16

705,600

7.1

DTS

digital

96,000

24

2,304,000

23.0

Dolby Digital

digital

SACD

digital

3,500,000

35.0

DVD-Audio

digital

88,000
96,000
96,000
192,000

16
20
24
24

1,408,000
1,920,000
2,304,000
4,608,000

14.1
19.2
23.0
46.1

Dolby True HD

digital

192,000

24

4,608,000

46.1

Satellite Radio
(mp3)

digital

iPod (mp3) 16 kbs
320 kbs

digital

16,000
320,000

0.2
3.2

wave files
16bit, 32k
23, 44.1k
24, 96k

digital

32,000
44,100
96,000

16
24
24

512,000
1,058,000
2,304,000

5.1
10.6
23.0

Calculation MethodConverting analog performance levels to a digital
equivalent involves developing bit rate (sampling frequency) and bit depth (bits
per sample) from the analog data. Since the sampling frequency for the CD format
is 44.1 kHz -- roughly double the highest frequency (20 kHz) it can reproduce,
the analog equivalent sampling frequency is calculated to be double the highest
frequency that medium can deliver. For the bit size figure, a 6dB difference in
dynamic range is taken to be equal to 1 bit so an analog medium with a dynamic
range of 60dB has an equivalent bit size to a 10 bit digital signal.

The bit depth times the sampling rate per second equals the
number of bit per second the medium can deliver. This number divided by 100,000
for brevity is its Fidelity Potential Index. How fully the fidelity potential of
each medium is exploited by the format structure and electronics limitations
could be covered only by an extremely drawn out discussion so here, briefly
below is a very truncated list of caveats.

Formats And Specifications Not IncludedMany formats both analog and digital were not
included. Digital formats like Dolby ProLogic which are lossy (i.e. they drop
bits and then try to re-construct the signal to make the signal more compact)
are not included due to the a huge amount of guess work involved. We have not
included frequency response and dynamic range figures for the digital formats -
only their sampling frequencies and bit rates.

Column DescriptionsBit Depth - a sample of the musical waveform at one
point in time can be represented by one single byte of information. The
resolution of this byte (the number of bits that it can have) dictates the
dynamic range of the signal. The more bits, the greater the number of possible
levels which means louder loud passages and quieter silences. The range of the
dynamics in the music can be much better represented by a 24 bit system than an
8 bit system.

Sampling Frequency - how often the bits are represented. The
more often they are represented the higher the frequency they can represent.
Sampling 2,000 times a second cannot represent a 5 kHz signal. A waveform must
be represented by at least two data points per cycle so the minimum sampling
frequency required to cover the highest level of human hearing (20 kHz) would be
40 kHz.

Format Descriptions And CaveatsA sound signal starts out as an analog waveform - the
original musical note - and finishes as an analog waveform - the sound that is
reproduced for the listeners ears. The fidelity of a recording format is
dependent not only on the raw ability of its core engine to capture high dynamic
range and broad frequency response but on its ability to handle analog to
digital conversions and processing of the recorded signal.

The potential inherent in one medium does not guarantee sound
quality superior over another medium of lower potential capability as music
production standards vary immensely as does implementation of high standards of
engineering in the recording and reproduction equipment.

Dynamic range is not signal to noise. Digital systems are
inherently noise free. Any noise comes from their associated electronics, not
their media. Analog systems, with their different types of mechanical noise
(tape hiss, record ticks and pops) have a signal to noise level far smaller than
their ultimate dynamic range.

Digital systems use various forms of filters in their
recording and playback processes. These filters can introduce distortions in the
audible frequency range. One of the most famous examples of this is the
"brick wall" filters used above 20kHz on CDs. Early implementations of
this introduced various phase anomalies down as far as 10kHz or even lower.